This modules provides a partial access to Entrez databases such as
Pubmed, Gene or Protein. The API proposed by the NCBI is based on HTTP
requests, and this modules contains a couple of functions to ease the
construction of appropriate URLs. This module also offers a more
high-level access, with parsers for the answers from Entrez.

Databases in Entrez can be seen as collections of records, each
record representing an object of the database. The basic usage of
the low-level API is first to search a database with the esearch
utility. Given a query string, esearch will return a collection
of identifiers. These identifiers are then used to fetch the
actual records with the efetch utility. These two operations are
done in one call with the high-level API.